John P. Smol

Tracking Environmental Change Using Lake Sediments

Part I: Introduction, Numerical Overview, and Data-Sets. 1. The march towards the quantitative analysis of palaeolimnological data 2. Overview of numerical methods in palaeolimnology 3. Data-sets Part II: Numerical Methods for the Analysis of Modern and Stratigraphical Palaeolimnological Data 4. Introduction and overview of Part II 5. Exploratory data analysis and data display 6. Assessment of uncertainties associated with palaeolimnological laboratory methods and microfossil analysis 7. Clustering and partitioning 8. From classical to canonical ordination 9. Statistical learning in palaeolimnology Part III: Numerical Methods for the Analysis of Stratigraphical Palaeolimnological Data 10. Introduction and overview of Part III 11. Analysis of stratigraphical data 12. Estimation of age-depth relationships 13. Core correlation 14. Quantitative environmental reconstructions from biological data 15. Analogue methods in palaeolimnology 16. Autocorrelogram and periodogram analyses of palaeolimnological temporal-series from lakes in central and western North America to assess shifts in drought conditions Part IV: Case Studies and Future Developments in Quantitative Palaeolimnology 17. Introduction and overview of Part IV 18. Limnological responses to environmental changes at inter-annual to decadal time scales 19.Human impacts - applications of numerical methods to evaluate surface-water acidification and eutrophication 20.Tracking Holocene climatic change with aquatic biota from lake sediments: case studies of commonly used numerical techniques 21. Conclusions and future challenges.- Glossary, acronyms, and abbreviations Index

The diatoms: applications for the environmental and earth sciences.

Part I. Introduction: 1. Applications and uses of diatoms: prologue Eugene F. Stoermer and John P. Smol Part II. Diatoms as Indicators of Environmental Change in Flowing Waters and Lakes: 2. Assessing environmental conditions in rivers and streams with diatoms R. Jan Stevenson and Yangdong Pan 3. Diatoms as indicators of hydrologic climatic change in saline lakes S. C. Fritz, B. F. Cumming, F. Gasse and K. R. Laird 4. Diatoms as mediators of biogeochemical silica depletion in the Laurentian Great Lakes Claire L. Schelske 5. Diatoms as indicators of surface water acidity Richard W. Battarbee, Donald F. Charles, Sushil S. Dixit and Ingemar Renberg 6. Diatoms as indicators of lake eutrophication Roland I. Hall and John P. Smol 7. Continental diatoms as indicators of long-term environmental change J. Platt Bradbury 8. Diatoms as indicators of water-level change in freshwater lakes Julie A. Wolin and Hamish C. Duthie Part III. Diatoms as Indicators in Extreme Environments: 9. Diatoms as indicators of environmental change near Arctic alpine treeline Andre F. Lotter, Reinhard Pienitz and Roland Schmidt 10. Freshwater diatoms as indicators of environmental change in the high Arctic Marianne S. V. Douglas and John P. Smol 11. Diatoms as indicators of environmental change in Antarctic freshwaters S. A. Spaulding and D. M. McKnight 12. Diatoms of aerial habitats Jeffery R. Johansen Part IV. Diatoms as Indicators in Marine Estuarine Environments: 13. Diatoms as indicators of coastal paleoenvironments relative to sea-level change Luc Denys and Hein de Wolf 14. Diatoms and environmental change in brackish waters Pauli Snoeijs 15. Applied diatom studies in estuaries and shallow coastal environments Michael J. Sullivan 16. Estuarine paleoenvironmental reconstructions using diatoms Sherri Rumer Cooper 17. Diatoms and marine paleoceanography Constance Sancetta Part V. Other Applications: 18. Diatoms and archaeology Steve Juggins and Nigel Cameron 19. Diatoms in oil gas exploration William N. Krebs 20. Forensic science diatoms A. J. Peabody 21. Toxic harmful marine diatoms Greta A. Fryxell and Maria Celia Villac 22. Diatoms as markers of atmospheric transport Margaret A. Harper 23. Diatomite David M. Harwood Part VI. Conclusions: Epilogue Eugene F. Stoermer and John P. Smol Glossary Index.

EFFECTS OF CLIMATE CHANGE ON THE FRESHWATERS OF ARCTIC AND SUBARCTIC NORTH AMERICA

Region 2 comprises arctic and subarctic North America and is underlain by continuous or discontinuous permafrost. Its freshwater systems are dominated by a low energy environment and cold region processes. Central northern areas are almost totally influenced by arctic air masses while Pacific air becomes more prominent in the west, Atlantic air in the east and southern air masses at the lower latitudes. Air mass changes will play an important role in precipitation changes associated with climate warming. The snow season in the region is prolonged resulting in long-term storage of water so that the spring flood is often the major hydrological event of the year, even though, annual rainfall usually exceeds annual snowfall. The unique character of ponds and lakes is a result of the long frozen period, which affects nutrient status and gas exchange during the cold season and during thaw. GCM models are in close agreement for this region and predict temperature increases as large as 4°C in summer and 9°C in winter for a 2 × CO2 scenario. Palaeoclimate indicators support the probability that substantial temperature increases have occurred previously during the Holocene. The historical record indicates a temperature increase of > 1°C in parts of the region during the last century. GCM predictions of precipitation change indicate an increase, but there is little agreement amongst the various models on regional disposition or magnitude. Precipitation change is as important as temperature change in determining the water balance. The water balance is critical to every aspect of hydrology and limnology in the far north. Permafrost close to the surface plays a major role in freshwater systems because it often maintains lakes and wetlands above an impermeable frost table, which limits the water storage capabilities of the subsurface. Thawing associated with climate change would, particularly in areas of massive ice, stimulate landscape changes, which can affect every aspect of the environment. The normal spring flooding of ice-jammed north-flowing rivers, such as the Mackenzie, is a major event, which renews the water supply of lakes in delta regions and which determines the availability of habitat for aquatic organisms. Climate warming or river damming and diversion would probably lead to the complete drying of many delta lakes. Climate warming would also change the characteristics of ponds that presently freeze to the bottom and result in fundamental changes in their limnological characteristics. At present, the food chain is rather simple usually culminating in lake trout or arctic char. A lengthening of the growing season and warmer water temperature would affect the chemical, mineral and nutrient status of lakes and most likely have deleterious effects on the food chain. Peatlands are extensive in region 2. They would move northwards at their southern boundaries, and, with sustained drying, many would change form or become inactive. Extensive wetlands and peatlands are an important component of the global carbon budget, and warmer and drier conditions would most likely change them from a sink to a source for atmospheric carbon. There is some evidence that this may be occurring already. Region 2 is very vulnerable to global warming. Its freshwater systems are probably the least studied and most poorly understood in North America. There are clear needs to improve our current knowledge of temperature and precipitation patterns; to model the thermal behaviour of wetlands, lakes and rivers; to understand better the interrelationships of cold region rivers with their basins; to begin studies on the very large lakes in the region; to obtain a firm grasp of the role of northern peatlands in the global carbon cycle; and to link the terrestrial water balance to the thermal and hydrological regime of the polar sea. Overall, there is a strong need for basic research and long-term monitoring.

Rapid response of treeline vegetation and lakes to past climate warming

FUTURE greenhouse warming is expected to be particularly pronounced in boreal regions1, and consequent changes in vegetation in these regions may in turn affect global climate2–4. It is therefore important to establish how boreal ecosystems might respond to rapid changes in climate. Here we present palaeoecological evidence for changes in terrestrial vegetation and lake characteristics during an episode of climate warming that occurred between 5,000 and 4,000 years ago at the boreal treeline in central Canada. The initial transformation — from tundra to forest-tundra on land, which coincided with increases in lake productivity, pH and ratio of inflow to evaporation — took only 150 years, which is roughly equivalent to the time period often used in modelling the response of boreal forests to climate warming5,6. The timing of the treeline advance did not coincide with the maximum in high-latitude summer insolation predicted by Milankovitch theory7, suggesting that northern Canada experienced regionally asynchronous middle-to-late Holocene shifts in the summer position of the Arctic front. Such Holocene climate events may provide a better analogue for the impact of future global change on northern ecosystems than the transition from glacial to nonglacial conditions.

Crossing the final ecological threshold in high Arctic ponds

A characteristic feature of most Arctic regions is the many shallow ponds that dot the landscape. These surface waters are often hotspots of biodiversity and production for microorganisms, plants, and animals in this otherwise extreme terrestrial environment. However, shallow ponds are also especially susceptible to the effects of climatic changes because of their relatively low water volumes and high surface area to depth ratios. Here, we describe our findings that some high Arctic ponds, which paleolimnological data indicate have been permanent water bodies for millennia, are now completely drying during the polar summer. By comparing recent pond water specific conductance values to similar measurements made in the 1980s, we link the disappearance of the ponds to increased evaporation/precipitation ratios, probably associated with climatic warming. The final ecological threshold for these aquatic ecosystems has now been crossed: complete desiccation.

Marked post-18th century environmental change in high-arctic ecosystems.

Paleolimnological data from three high-arctic ponds on Cape Herschel, Ellesmere Island, Canada, show that diatom assemblages were relatively stable over the last few millennia but then experienced unparalleled changes beginning in the 19th century. The environmental factors causing these assemblage shifts may be related to recent climatic warming. Regardless of the cause, the biota of these isolated and seemingly pristine ponds have changed dramatically in the recent past and any hopes of cataloging natural assemblages may already be fruitless.

Fisheries productivity in the northeastern Pacific Ocean over the past 2,200 years

Historical catch records suggest that climatic variability has had basin-wide effects on the northern Pacific and its fish populations, such as salmon, sardines and anchovies. However, these records are too short to define the nature and frequency of patterns. We reconstructed ∼2,200-year records of sockeye salmon abundance from sediment cores obtained from salmon nursery lakes on Kodiak island, Alaska. Large shifts in abundance, which far exceed the decadal-scale variability recorded during the past 300 years, occurred over the past two millennia. A marked, multi-centennial decline in Alaskan sockeye salmon was apparent from ∼100 BC to AD 800, but salmon were consistently more abundant from AD 1200 to 1900. Over the past two millennia, the abundances of Pacific sardine and Northern anchovy off the California coast, and of Alaskan salmon, show several synchronous patterns of variability. But sardines and anchovies vary out of phase with Alaskan salmon over low frequency, which differs from the pattern detected in historical records. The coherent patterns observed across large regions demonstrate the strong role of climatic forcing in regulating northeastern Pacific fish stocks.

Paleolimnology: an important tool for effective ecosystem management

Effective management of aquatic resources requires long-term environmental data. However, because long-term observations are rarely available, indirect proxy methods must be used to substitute for these missing historical data sets. Major advances have been made in paleolimnology over the last decade, and many of these advances can be applied directly to integrated and cost-effective assessments of aquatic ecosystem health. This commentary uses the analogy of human health to argue that paleolimnological data provide information crucial to the decision-making processes of ecosystem managers.

Setting minimum head capsule abundance and taxa deletion criteria in chironomid-based inference models

Criteria for removing training set lakes and taxa in chironomid‐based inference models, due to low abundances, have largely been ad hoc. We used an anoxia inference model and a hypolimnetic oxygen model from south‐central Ontario to determine what effect subfossil head capsule abundance and taxa deletion criteria have on fossil inference statistics. Results from six training set lakes suggest that a minimum abundance of 40–50 head capsules is sufficient for use in inference models, however more diverse samples likely require more than 50 head capsules. Taxa deletion criteria substantially improved the predictive ability of inference models (lowered the root mean squared error of prediction (RMSEP)). The common practice of including taxa with only ≥ 2% abundance in at least two lakes was one of the deletion criteria that much improved inference models. Similar deletion criteria, such as ≥ 2% in at least 3 lakes and ≥ 3% in at least 1 lake, produced comparable improvements (up to 18% reduction in RMSEP).

The Widespread Threat of Calcium Decline in Fresh Waters

Calcium concentrations are now commonly declining in softwater boreal lakes. Although the mechanisms leading to these declines are generally well known, the consequences for the aquatic biota have not yet been reported. By examining crustacean zooplankton remains preserved in lake sediment cores, we document near extirpations of calcium-rich Daphnia species, which are keystone herbivores in pelagic food webs, concurrent with declining lake-water calcium. A large proportion (62%, 47 to 81% by region) of the Canadian Shield lakes we examined has a calcium concentration approaching or below the threshold at which laboratory Daphnia populations suffer reduced survival and fecundity. The ecological impacts of environmental calcium loss are likely to be both widespread and pronounced.